Tears coating the eyeball surface have a three-layer structure consisting of a mucous layer comprising mucin, an aqueous layer, and an oily layer, from the eyeball side. Between the aqueous layer and the oily layer, an amphiphilic lecithin layer is known to exist and stabilize tears by acting as a bridge between the two layers (Nihon No Ganka Vol. 74, No. 6, 569-572, 2003).
Since lecithin is a tear constituent, ophthalmic compositions comprising lecithin have been proposed in recent years. For example, WO 2006/009112 discloses an aqueous eyedrop for prevention or treatment of dry eyes, the solution comprising castor oil and lecithin. Also, WO 2005/025539 discloses an ophthalmic composition for contact lenses, the composition comprising a refrigerant and/or chlorobutanol and forming an oil-in-water emulsion due to the presence of lecithin.